One thing is funny, though...apparently, the new cosmology brings along a greater shift towards a law/chaos dichotomy again, and away from good/evil. Think about it...the Astral Sea harbors all the Astral Domains, along with the Nine Hells, while the Elemental Tempest has the great chaotic mishmash of elements and the Abyss in the middle. Sandwiched inbetween those two is the Prime. Somehow I'm getting this "Gods vs. Eternal Chaos" vibe here, with mortals as pawns and helpers in the middle. Sure, there's bound to be some chaotic gods in the Astral Sea as well, but I have the impression that most Chaos will be concentrated "below" the Prime, so to speak, and most of the order types "above".
I wouldn't be surprised if they brought Mystara back from the dead as a new 4E campaign setting, or at least cribbed a lot of inspiration from it. Somebody like Asmodeus would be a lawful (evil) immortal in the Sphere of..hmmm, Energy maybe...while Orcus and Demogorgon were already in there as immortals of Entropy. Funny...the whole cosmology would fit in there pretty easy. Looks like I might take a peek at any 4E MotP, when it comes out.